Brocade BigIron RX Series Configuration Guide - Manual (Page 938)

860 BigIron RX Series Configuration Guide
53-1002484-04
Enabling next-hop recursion
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The route to the next-hop gateway is a BGP route, not an IGP route, and thus cannot be used to
reach 240.0.0.0/24. In this case, the device tries to use the default route, if present, to reach the
subnet that contains the BGP route’s next-hop gateway.
Example when recursive route lookups are enabled
When recursive next-hop lookups are enabled, the device recursively looks up the next-hop
gateways along the route until the device finds an IGP route to the BGP route’s destination. Here is
an example.
The first lookup results in an IBGP route, to network 102.0.0.0/24.
Since the route to 102.0.0.1/24 is not an IGP route, the device cannot reach the next hop through
IP, and thus cannot use the BGP route. In this case, since recursive next-hop lookups are enabled,
the device next performs a lookup for 102.0.0.1’s next-hop gateway, 10.0.0.1.
BigIron RX# show ip route 240.0.0.0/24
Total number of IP routes: 37
Network Address Gateway Port Cost Type
0.0.0.0 10.0.0.202 1/1 1 S
BigIron RX# show ip bgp route
Total number of BGP Routes: 5
Status A:AGGREGATE B:BEST b:NOT-INSTALLED-BEST C:CONFED_EBGP D:DAMPED
H:HISTORY I:IBGP L:LOCAL M:MULTIPATH S:SUPPRESSED
Prefix Next Hop Metric LocPrf Weight Status
1 0.0.0.0/0 10.1.0.2 0 100 0 BI
AS_PATH: 65001 4355 701 80
2 102.0.0.0/24 10.0.0.1 1 100 0 BI
AS_PATH: 65001 4355 1
3 104.0.0.0/24 10.1.0.2 0 100 0 BI
AS_PATH: 65001 4355 701 1 189
4 240.0.0.0/24 102.0.0.1 1 100 0 BI
AS_PATH: 65001 4355 3356 7170 1455
5 250.0.0.0/24 209.157.24.1 1 100 0 I
AS_PATH: 65001 4355 701
BigIron RX# show ip route 102.0.0.1
Total number of IP routes: 38
Network Address Gateway Port Cost Type
102.0.0.0 10.0.0.1 1/1 1 B
AS_PATH: 65001 4355 1
BigIron RX# show ip bgp route 102.0.0.0
Number of BGP Routes matching display condition : 1
Status A:AGGREGATE B:BEST b:NOT-INSTALLED-BEST C:CONFED_EBGP D:DAMPED
H:HISTORY I:IBGP L:LOCAL M:MULTIPATH S:SUPPRESSED
Prefix Next Hop Metric LocPrf Weight Status
1 102.0.0.0/24 10.0.0.1 1 100 0 BI
AS_PATH: 65001 4355 1